Project Summary The goal of the proposed work is to create bacteria that detect the level of a micronutrient (vitamin or mineral) in a sample, with ultimate application to human blood tests. The micronutrient to be detected is zinc. These cells will enable the later development of minimal-equipment testing of blood zinc levels in remote, resource-poor locations, a significant improvement in both the time and cost necessary using current state-of-the-art methods. The cells use a genetic circuit controlled by zinc-sensitive transcription factors to produce different colored pigment based on the zinc concentration in the sample, indicating whether zinc levels are acceptable or low. Thus, the cells function as a sort of easy-to-read ?bacterial litmus test?. Strong preliminary work supports the likelihood of our success. The first aim involves creating the bacterial strain capable of producing three different pigments in response to different levels of extracellular zinc. The second aim involves making the existing circuit repress pigment production until the assay is performed, allowing for the pre-culture of colorless cells that will enable fast coloration and overcome obstacles to sensor cell survival in human blood samples.The third aim consists of tuning the cells' performance when grown in actual blood samples, since work to date has used laboratory growth medium which may yield different results than growth in the long-term target samples. This project will yield the underlying technology that can be used for the first-ever bacterial blood test for low-resource settings to provide population-level assessment of micronutrient status. By being low-cost and essentially point-of-care, such a long-term result would enable nutritional epidemiologists and policymakers to make more informed decisions about nutritional interventions, as well as to assess the success of interventions after the fact, potentially improving the health of millions of undernourished people. Moreover, the pigment-producing genetic circuit establishes a framework that can be applied for the development of other micronutrient sensors using different nutrient-binding proteins, potentially allowing a whole panel of inexpensive tests.